The mechanism behind the formation of dye images in a silver halide color photographic material is that an aromatic primary amine developing agent, while reducing silver halide grains in the exposed photographic material, is oxidized and the resulting oxidized product reacts with a coupler already present in the silver halide color photographic material so as to form a dye. Color reproduction in this case depends commonly on the subtractive process using three couplers which respectively form yellow, magenta and cyan dyes. These couplers are added to silver halide emulsion layers after they are dissolved in a substantially water-soluble high-boiling organic solvent, optionally in combination with an auxiliary solvent.
There are several requirements that must be met by the couplers: first, they must have high solubility in high-boiling organic solvents, and they should be highly dispersible in silver halide emulsions and the prepared dispersion should remain stable without causing the precipitation of the couplers; secondly, the couplers should have sufficiently good spectral absorption characteristics and color tone to produce sharp dye images over a broad color reproduction range; and thirdly, the couplers should produce dye images which are fast to light, heat and moisture. Particularly, the cyan couplers are required of improvement in two points, namely, that the absorption in the spectral region other than the main spectral region of the cyan couplers is less, and that the cyan dye images produced are resistant to light, heat and moisture. As cyan couplers, 2,5-diacylaminophenolic cyan couplers are known which have an acylamino group as a substituent on the 2- and 5-positions of the phenol ring, and cyan couplers of this type are shown in U.S. Pat. No. 2,895,826, as well as Japanese Unexamined Published Patent Application Nos. 112038/1975, 109630/1978 and 163537/1980. When such 2,5-diacylaminophenolic cyan couplers are used, the reproduction of green color becomes good because of low sub-absorption in the region of 400-450 nm, and also good recoloring properties are exhibited. Further, the dark discoloration such as resistance to heat and moisture likewise becomes good. Thus, with the use of such cyan coupler, cyan dye images can be greatly improved in discoloration balance of the cyan, magenta and yellow colors.
However, these cyan couplers have the following disadvantages: (1) they have a high minimum spectral density (hence, low brightness) in the region of 450-480 nm, thereby providing a small color reproduction range, and, additionally, the high absorption in the 500-550 nm range causes poor reproduction of the green color; (2) the couplers do not have adequate resistance to light; and (3) the couplers are low in dissolvability and dispersion stability. Therefore, these cyan couplers do not fully meet the fundamental properties required of couplers in general.